Two-component synergistic antioxidant system for polyolefins

ABSTRACT

An epoxide resin of the bisphenol-A type having the general formula-   WHERE N IS FROM 0 TO 18 AND LITHARGE (PbO) when mixed together cooperate synergistically to provide a very effective antioxidant for some polyolefins and chlorinated polyolefin resins.   D R A W I N G

United States Patent 1 Abu-isa 1 Feb. 18, 1975 1 TWO-COMPONENT SYNERGISTIC ANTIOXIDANT SYSTEM FOR POLYOLEFINS [75] Inventor: Isrnat A. Abu-Isa, Birming ham,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Jan. 23, 1974 [21] App1. No.: 435,720

[52] US. Cl..... 260/837 R, 260/42l28, 260/45.75 R

51 Int. Cl C08g 45/04 [58] Field of Search 260/42.28, 45.75 R, 837 R [56] References Cited UNITED STATES PATENTS 2,467,550 4/1949 Fletcher 260/45.75 R

2,480,008 8/1949 Anderson 260/41 R 2,564,194 8/1951 Johannes de Me 260/45.8 A 3,139,414 6/1964 Ranalli 260/837 R FOREIGN PATENTS OR APPLlCATIONS 3/1958 Germany Primary ExaminerJames H. Derrington Attorney, Agent, or FirmGeorge A. Grove [57] ABSTRACT An epoxide resin of the bisphenol-A type having the general formulaon on, o

2 Claims, No Drawings I 1 TWO-COMPONENT SYNERGlSTlC ANTIOXIDANT SYSTEM FOR POLYOLEFINS where n has any value from O'to about 18. The epoxide preferably constitutes about 45*perc'ent of the total synergistic antioxidant additive mixture. However, the epoxide may be present within a suitable range offrom about 35 percent by weight to about 50 percent'by weight of the total of the two materials. The balance of the antioxidant system is litharge (PbO). This antioxiwhere n is from 0 to 18 and litharge (PbO). The result is a remarkable increase in the oxidation resistance of the aforementioned polymers as reflected in both an increase in the induction time, during which little or no oxygen absorption by the resin occurs, and a decrease in the rate of oxygen absorption once the induction period has lapsed.

BACKGROUND or THE INVENTION Most organic polymers including the thermoplastic polyolefin polymers are susceptible to degradation reactions during aging. The most prevalent of these reactions is oxidation which may result'in excessive cross,

linking and embrittlement but it usually leads to chain scission which causes the material to soften and may literally destroy the resins structural integrity. In either event, a degraded polymer is of little use, as it no longer has the engineering and decorative properties which made it particularly suited for a given application.

In the past, the oxidative degradation reaction has been slowed or delayed by the use of rather. elaborate organic molecules such as the hindered phenols to neutralize the reactive oxygen radical by either a free radical or an ion exchange mechanism. These materials are conventionally used in concentrations of less than five percent and since they are not a part of the polymer matrix they may have a deleterious effect on the structural properties of the material. In addition, these antioxidants may be quite expensive since often times their molecular structure must be tailored to fit a given application.

It is an object of this invention to provide a novel antioxidant composition which has both improved effectiveness and lower cost for use in some polyolefin resins.

It is a further object to provide a novel synergistic antioxidant which utilizes the interaction and combined effect of an epoxide resin of the bisphenol-A type and lead oxide (PbO) to provide improved antioxidant protection for certain polyolefin materials.

SUMMARY OF THE INVENTION 0 ca es-ea dant mixture is preferably uniformly distributed throughout the resin in which it is employed.

I intend that this novel antioxidant mixture be used only in polyethylene, polypropylene, chlorinated polyethylene or mixtures thereof. Asis known chlorinated polyethylene is a polymer having an aliphatic carbon backbone (like polyethylene) with chlorine. atoms randomly replacing the hydrogen atoms along the chain.

The terms antioxidant and stabilizer have. in the past, been loosely used interchangeably, and therefore the features which distinguish these two functions have been obscured. More precisely, a stabilizer'does not act to inhibit the initial reaction of the polymer molecule with a foreign substance. however, it does prevent the reaction product of that initial reaction from further degrading the polymer. For example, a stabilizer might not inhibit-the dehydrochlorination of poly(vinyl chloride), however astabilizer will inhibit the subsequent attack of the polymer by hydrogen chloride'which is a product of the initial dehydrochlorination. Comparapolyolefin materials. In this Table the first column is .the polymer being tested and the second column shows the induction period, during which there is littleor no oxygen absorptiomThe third column lists the rate of oxygen absorption once the induction period has lapsed; the maximum absorption rate is reported and this usually occurs immediately after the induction period.

The absorption data are indicative of the rate of oxidative degradation since the oxidation reaction 7 removes free oxygen from the polymer matrix and thereby creates a concentration gradient allowing the polymer to absorb oxygen from the surrounding atmosphere. The laws of diffusion require a concentration gradient for a mass transfer phenomenon, which in this case is absorption, to occur. Therefore, the-rate of oxidative degradation is directly proportional to the rate of oxygen absorption. Accordingly, the longer'the induction period and the lower the rate of oxygen absorpfectof these two ingredients when they are used totion the more effective the antioxidant. material were milled on a two roll mill to give the stan- The specific antioxidant used in the polymeric resins dard formulation the same mechanical and thermal hislisted in Table I was a mixture of parts by weight litory as the test samples. After the milling operation. tharge and 4 parts by weight of an epoxy having the thin slabs l-IV2 mils thick were molded from the polygeneral formula- 5 mer.

CH i n CH3 where n was 0.15. Where used, the antioxidant mixture To prepare the test samples, 182 grams of chlorinaconstituted about 9 percent by weight of the polymeric ted p ly thylene were mixed with 8 grams of an epoxm ide resin having the formula- 0 cH 0H ca, 0 l l l cn -cn-cn O@C|@OCH -CHCH o.-@-cl-@-o-cu -cH-cn cH I 11 ca,

Table I shows that the addition of the subject antioxi- I where n 0.15 and grams of litharge (PbO). This dant system at the preferred concentration of about 9 mixture was then milled and molded as described percent by weight reduces the rate of oxygen absorpabove. tion and therefore the rate of oxidative degradation by The oxygen absorption of each polymer composition was measured using an all glass apparatus. Separate at least one order of magnitude after the induction pe- V samples of each polymer compound were heated in the riod had elapsed.

TABLE I l The Effectiveness of the Subject Antioxidant in Various Polymers Which Were Aged in Pure Oxygen at Various Temperatures Aging Induction Rate of Post Induction Oxygen Temperature Period Absorption (Milliliters of Oxygen Polymer System C. (Hours) per Gram of Polymer per Hour) 1. Chlorinated Polyethylene (CPE) ISO 0 29.0 165 0 39.1 (PE Antioxidant (9%) 150 15 L8 I 3 7.0 I (I 24.1) 2. Polyethylene (P/li) (1 5H) P/l-I +-Antioxidnnt (994) I50 (14 3.7 3. Polypropylene (P/P) I51) t) 563.0 PIP Antioxidant (9%) I50 6 I51 7 DETAILED DESCRIPTION OF THE INVENTION closed apparatus at 150C and C using pure oxygen as the atmosphere. The induction periods of the two compositions along with the rates of oxygen absorption were measured by a technique which is fully described in the Journal of Polymer Science, Part Al. Vol. 8(4), p. 961, 1970, written by the inventor herein. This article is incorporated herein by reference; the data from this example are-also tabulated in Table I.

The effectivenessof the antioxidant system at a concentration of 9 percent is clearly demonstrated by both In accordance with my invention, these and other advantages will be more apparent in view of the following detailed description including specific examples. 45

Although epoxy resins have been disclosed as antioxidants for some polymers, the examples discussed below will clearly demonstrate'that the addition of the litharge at the preferred concentration greatly increases their effectiveness in the subject polyolefin 50 compositions. These examples also show that litharge (PbO) alone is only slightly effective as an antioxidant reduction of the rate t hich ox and that there 15 more than the slmple cumulative efa W ygen was absorbed by the material after the induction period has lapsed.

gether as an antioxidant system. This combined effect 55 EXAMPLE 2 proPerly termed Synerglsm- The Stabilization of Polyethylene In this example, four polymer compositions were for- 4 EXAMPLE 1 mulated using polyethylene as the base resin and then The Stabilization of Chlorinated Polyethylene ,0 processed using the same antioxidant composition and In this example. two formulations were compounded testing procedures as described in Example 1, except to test the effectiveness of the litharge-epoxy antioxithat theoxidation evaluations were conducted at only dant mixture in a chlorinatedpolyethylene. The polyone temperature-150C. The first formulation served mer containing no antioxidant was used as a standard as a standard and was pure hi-density polyethylene havand the same blending and testing procedures were 'fol- 5 ing no antioxidant. The second formulation consisted lowed with each formulation. of 192 grams of polyethylene and 8 grams of the epox- This standard formulation was a chlorinated polyethide resin which was used in Example 1. The third forylene having no antioxidant additive. 200 grams of this mulation consisted of grams of the hi-density polythe increase in the induction period and the dramatic ethylene and grams of litharge (PbO). Finally, the fourth formulation consisted of 182 grams of hi-density polyethylene, 8 grams of the epoxide resin and 10 grams of litharge.

The oxygen absorption data on these four formulations are illustrated in Table 11 and they clearly demonstrate two important aspects of this invention. First, this data shows that the antioxidant system of this invention is effective in inhibiting the oxidation of polyethylene Secondly, it is evident from this Table that this effect is not simply a cumulative effect of the two ingredients litharge and epoxide resins and, therefore, there is definitely a synergism acting in this system.

TABLE ll example, I tried tin oxide and antimony oxide because like lead oxide they both are bivalent. Then I tried acid acceptors such as dibutyltinmaleate and magnesium oxide because lead oxide is also an acid acceptor. Finally, I tried other random lead compounds such as lead acetate. These formulations were blended and compounded according to the procedures described in Example 1 and the oxygen absorption properties were also measured in accordance with that procedure. The test results of these various compounds are shown in Table Ill and unfortunately there was no clear indication of the possible chemical mechanism which may be operative in this system. In fact, none of the other com- Degradation of Polyethylene Compounds at 150C in Pure Oxygen lnduetion Rate of Oxygen Absorption Period (Milliliters of Oxygen per Compound (Hours) (iram of Polymer per Hour) 1. Pure Polyethylene O 51.1) 2. Polyethylene 4% epoxide resin 1) 38.5 3. Polyethylene 57: PbO 6 13.8 4, Polyethylene 5% PbO 4?! epoxide resin 64 3.7

EXAMPLE 3 The Stabilization of Polypropylene Using the procedures described in Example 1, sam ples of a pure polypropylene having no antioxidant and a polypropylene stabilized with the subject antioxidant pounds even approached the effectiveness of the system which is the subject of this invention, and there is no trend in the data to indicate a possible mechanism.

The percentage values in Table III by the respective additives are on a weight basis and'based upon the weight of polypropylene.

TABLE Ill The Effectiveness of Potential Antioxidant Systems in Polypropylene at 150C. and Pure Oxygen EP is the subject epoxide resin *SAS refers to subject antioxidant system system were prepared. The'oxygen absorption tests were performed according to the same procedures that were described in Example 1, and the data is recorded in Table I. This novel antioxidant proved to be very effective in reducing the oxygen absorption and therefore the oxidative degradation of the polypropylene resin.

A series of experiments were run in an effort to de fine the mechanism by which the litharge and the epoxide resin combined to provide antioxidant protection to the polyoletin resins. To do this, I replaced the litharge with various compounds having similar properties. For

While my invention has been described in terms of certain preferred embodiments, it will be appreciated that'other forms thereof could be readily adapted by one skilled in the art. Therefore, the scope of my invention is not limited to the specific embodiments illustrated.

What is claimed is:

1. An oxidation resistant polyolefm composition comprising a polyoletin selected from the group consisting of polyethylene, polypropylene and chlorinated polyethylene, and two to fifteen percent by weight based on said polyolefin composition of an antioxidant, sisting of polyethylene, polypropylene and chlorinated said antioxidant consisting essentially of, by weight, polyethylene, and two to fifteen percent by weight from about 35 percent to about 50 percent of an ep xbased on said polyolefin composition of an antioxidant, ide having the general formulasaid antioxidant consisting essentially of, by weight,

. CH n CH where n is from to 18, and the balance litharge. from about 35 percent to 50 percent of an epoxide huv 2. An oxidation resistant polyolefin composition ing the general formulacomprising a polyolefin selected from the group conwhere n is fromO to l and the balance litharge.

. l= l= l 

1. AN OXIDATION RESISTANT POLYOLEFIN COMPOSITION COMPRISING A POLYOLEFIN SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE, POLYPROPYLENE AND CHLORINATED POLYETHYLENE, AND TWO TO FIFTEEN PERCENT BY WEIGHT BASED ON SAID POLYOLEFIN COMPOSITION OF AN ANTIOXIDANT, SAID ANTIOXIDANT CONSISTING ESSENTIALY OF, BY WEIGHT, FROM ABOUT 35 PERCENT TO ABOUT 50 PERCENT OF AN EPOXIDE HAVING THE GENERAL FORMULA-
 2. An oxidation resistant polyolefin composition comprising a polyolefin selected from the group consisting of polyethylene, polypropylene and chlorinated polyethylene, and two to fifteen percent by weight based on said polyolefin composition of an antioxidant, said antioxidant consisting essentially of, by weight, from about 35 percent to 50 percent of an epoxide having the general formula- 